We will guide you by OS. Please check the following.
Android
Whether the device is compatible with the Google Play Store
Devices that are not compatible with the Google Play Store are outside the scope of Teachme Biz support.
Related: Teachme Biz Recommended Environment
https://help.teachme.jp/hc/en-us/articles/14572215297305
Whether the Google account is correctly linked to the device being used
If the Google account and device are not properly linked, it may cause downloads to take longer or errors to occur.
Please check the sync status of your account and device with your company's IT department or Google Support.
iOS/Android
Whether app downloads are prohibited due to security settings
Your company's security settings may restrict the use of the Google Play Store or the downloading and installation of applications.
Please check with your company's IT department.
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Related: Are there things to check before purchasing Android devices in bulk or before starting to use the mobile app on Android devices?
https://help.teachme.jp/hc/en-us/articles/900005507766